So what sort of gear lube should you use in that WW2 jeep?
Or, why you’ll use GO 90 instead of SAE 140, which you can’t get.

This article has been extracted from Military Maintenance for MB/GPW 1941-1945. Originally appearing in WW2 Army Motors.

It was a very hot day in the ARMY MOTORS’ office. The Editor was mopping his face with next month’s ‘Contribution’ section and leering at Connie Rodd who was wearing a blue denim play-suit. Half-Mast had disappeared in the general direction of Bill’s Place, and the technicians sat in a circle an the floor playing a vicious game. of Parcheesi.

Suddenly two tiny men, one purple and one green, bath with pink mustaches and GI haircuts, leaped out of the ashtray, one yelling “NINETY”! and the other screaming “EIGHTY ONE-FORTY”. Beating each other over the head with paper clips, they scurried across the desk and under the telephone.

“Hmmm,” said Ed, pouring another beer.

“Looks like some more at that business about transfer case lubes.” “Caddington” he cried, painting a bony finger at Caddington, “Caddington, find out for once and for all WHY the men have to use GO 90 in transfer cases instead of SAE 140, on a day like this. People say the GO 90 causes transfer case leakage. Now, Caddington is not an ambitious man. If he were, he would have disappeared far thirteen days and thirteen nights, and returned with an article. Instead, he reached in his pocket, pulled out a grimy piece of paper labeled “Fargo Technical Bulletin #46G” and tossed it on the desk.

“Half-Mast said you’d ask, and there’s the answer”, he explained. Then he went back to sleep.

Well now, our Ed knows as well as you do that the reasons for using GO 90 instead of SAE 140 in transfer cases are mostly military. We don’t use any mare different varieties of lube in the army these days than we absolutely need; result, fewer kinds to supply, less shortages, everybody happier. And GO 90 is at least an acceptable substitute far SAE 140. But our expert has proof that GO 90 is better in transfer cases than SAE 140, because GO 90 is less likely to leak.

It’s all on account of the heat which SAE 140 generates when the vehicle is in operation. The gears of the transfer case have to do more work an the SAE 140 oil (because it’s a heavier oil), thus generating more heat in the oil. This lubricant usually warms up to a temperature of 235 to 260 degrees Fahrenheit, whereas GO 90 seldom gets above 190 to 210.

These higher temperatures have two results:

(1) The SAE 140 gets thinner us it gets hotter. By actual test, SAE 140 has the same viscosity at its operating temperature as GO 90 has at its operating temperature. Therefore, one will leak just as fast as the other if leakage is going to occur.

(2)More serious, the aver. heated SAE 140 will harden the oil seals, increasing the wear an the companion-flange hub, and thus actually cause leakage.

So. don’t be wishing for SAE 140, says our expert; be glad there’s none issued. Instead, if your vehicle is troubled with transfer-case leaks, try this:

(1) Check the lube level; maybe you have too much and the extra pressure is forcing the leaks. The level should be at the plug opening immediately after operation, or 1/2″ below the opening if the oil has had time to cool. Always check the vent in the transfer case to be sure it is open. This should be done each time the lube level is checked. If this vent is closed, leakage is bound to occur at the oil seals.

(2) Check the universal-joint companion flanges for up-and-down play in the bearings. If they are loose, remove the transfer case and get the bearings adjusted (you can’t get a proper adjustment while the case is still in the vehicle) .

(3) If it isn’t the bearings, remove the companion flanges and take a look at the hubs and ail seals. Replace any of either that are warn (treating new seals with ail to. soften the leather).

(4) If you have any doubt about the grade of lube in the transfer case, drain it out and install GO 90 far warm weather or GO 80 according to .the temperature chart as set up in the lube guide. Drain the transfer case should be done while it is hot, otherwise you won’t get all of the old oil out. If there is any question of dirt in the transfer case, it should be flushed with OE 10.

(5) Tighten the transfer-case mounting bolts.

Want to find out more about the WW2 jeep transfer case? Then you need this book – TM 9-1803B Power Train, Body, and Frame for Willys Overland Model MB and Ford Model GPW 1/4 Ton 4×4 Technical Manual.